(1) Field of the Invention
The present invention relates to an analog data signal switching network for cross-connecting analog data signals from a plurality of data transmitters to desired ones of a plurality of transmission lines.
(2) Description of the Prior Art
In an analog data transmission system where digital data signals are converted into analog data signals which are, in turn, transmitted to desired analog transmission lines, a switching network is used for cross-connecting or selectively connecting each one of a plurality of analog data signals as input channel signals from a plurality of data transmitters to a desired one of a plurality of output channel transmission lines according to a channel selection signal applied to the switching network. The channel selection signal is a signal for instructing to deliver a particular one of the input channel signals to a specific one of output channel transmission lines.
The switching network can contain a stand-by transmission line and a stand-by data transmitter. When a fault occurs in one of the data transmitters or one of the output channel transmission lines, the switching network can make the stand-by data transmitter or the stand-by transmission line take over the fault transmitter or the fault output channel transmission line by changing the channel selection signal.
A known switching network is a space switch having many relay contacts for switchingly coupling a particular one of the input channel signals to a specific one of the output channel transmission lines. The relay contacts have a problem in reliability for a long use.
As another known switching network, a time division switching network wherein each of the analog data signals as the input channel signals is converted to a digital signal by an analog-digital (A/D) converter and stored in a memory. The digital data signal is read from the memory to a digital-analog (D/A) converter connected to a desired or specific one of transmission lines. Then, the D/A converter converts the read digital data signal to a reproduced analog data signal and transmits the reproduced analog data signal to the specific output channel transmission line.
The time division switching network is small in size and good in reliability for a long use. However, use of A/D and D/A converters makes the switching network expensive. Further, the reproduced analog signal suffers from quantized noise generated in A/D conversion.